The invention relates to a humidity control system for a controlled atmosphere ("CA") container which uses moisture condensed from the feed air to an air separator to increase the humidity level in the CA container.
CA containers for the post-harvest processing, transporting, and storage of agricultural commodities are known in the art. The use of such containers is well established for the storage and transport of certain products such as apples and is growing for others. CA containers provide a longer shelf life than non-regulated containers for fruits and vegetables and result in optimum freshness at the place of ultimate destination.
Typically, CA containers utilize an air separation unit to remove oxygen and other naturally occurring gases from ambient air to produce a supply of gas having a nitrogen concentration of up to 99.5 percent. Precise amounts of O.sub.2 and CO.sub.2 are added to the nitrogen atmosphere in the CA container to create ideal storage conditions for the foodstuffs contained therein. A separate refrigeration unit cools the interior of the CA container to the desired temperature.
Often the CA container is a mobile unit which is hauled by truck cab, rail, or ship from the place of harvest to the ultimate destination. During this time, the air separation unit continually supplies nitrogen to the interior of the CA container in order to displace naturally occurring atmospheric gases and other gases which are given off by the foodstuffs during the ripening process and to replace nitrogen which escapes through leakage from the container itself. The air separator may use either pressure swing adsorption or hollow membrane technology in order to effect the necessary separation of nitrogen from the oxygen, carbon dioxide, and other constituents of atmospheric gas.
Feed air to the separator is dehumidified in order to increase the efficiency of the separator and product gas is typically dehydrated to a very dry condition as a result of the separation process itself. In the case of the controlled atmosphere storage of foods, relatively high humidity is usually desired and the humidity level should be kept within a narrow range. However, the availability of water and the space to store it in mobile units is minimal.
There is, accordingly, a need in the art for an air management system for a CA container in which the product gas in a CA container is humidified in order to provide optimum storage conditions in the container.